Process for the heat treatment of steel



Patented Oct. 23, 1934 UNITED STATES PATENT OFFICE Ellwood Ivins, Oak Lane, and Horace- S. Kircher,

Lansdale, Pa.--

No Drawing. Application February 16, 1934, Serial No. 711594 4 Claims.

This invention relates to a process for the heat treatment of drawn steel or other ferrous metals, and more particularly 'to a process especially adapted to heat treatment of drawn chrome 5 molybdenum steel tubing and is a continuation in part of our prior application Serial No. 613,552, filed May 25, 1932, for Process for the heat treatment of steel.

In the production of practically all forged or cold worked steel products, a heat treatment follows the completion of the article for the purpose of annealing, normalizing, bluing, or the like, particularly in the case of steels such as chrome molybdenum steels which are often employed in cold working processes and must be subjected to normalizing following such process. As is well known, heat treatment is destructive to all ferrous metals, with the possible exception of such metals as stainless steel, and eveninthe case of stainless steel heat treatment has often deleterious effects. With steels such as chrome molybdenum, however, the heat treatment usually results in fire scars, oxidation and cracking and an accompanying relatively high percentage of discards of the otherwise completed article.

We have discovered that the destruction of ferrous metal products in this final heat treatment may be entirely eliminated by coating the article prior to drawing preceding such heat treatment with a coating of a metal oxidizing at the heat treating temperature, and of such characteristies that will not physically or chemically combine with the ferrous metal at heat treating temperatures. Among such metals, tin, zinc and cadmium are suitable for use with practically all ferrous metals and are particularly adapted for use in connection with chrome molybdenum steels. The metal is preferably coated upon the article prior to a working step preceding heat treatment by an electro-plating process in which the article is left in the bath for about three minutes, or just sufficient to produce a very thin but appreciable and complete coating of the protecting metal thereon. Following this coating, the coated metal is subjected to a working step as, for example, drawing, which will subject the coating to extremely high pressure and preferably of such character that the coating is smoothed; that is to say, both reduced in thickness to the merest skim and dispersed over the surface of the metal so that it completely covers the same. The article is then placed in the oven for heat treatment and may be treated in an atmosphere oxidizing the coating at any temperature within its normal heat treating range without damage thereto. Employing this system with chrome molybdenum tubes which have been cold drawn and, therefore, require normalizing in order that crystalline deformations resulting from the drawing operation might be removed, internal strains might-be ,relieved'and the grains thereofequiaxed and the hardness and ductility of the material regulated, it has been found that temperatures as high as 1650 degrees F. could be employed and that the metal when removed from the furnace is almost entirely free of scale and absolutely immune from the usual fire marks, heavy scale and oxide and the surface scars and marks which are common in heat treating without the worked protective coating. Furthermore, it has been found that the physical properties of the steel themselves have been increased, tensile strength, elasticity and elongation having increased 10 to 30 per cent. This treatment, therefore, provides an ideal protection for ferrous metals and particularly ferrous metals, such as.

chrome molybdenum, which are employed in situations where the .greatest possible strength obtainable is desired.

While we prefer the use of tin in heat treatment of chrome molybdenum steels, the remaining metals mentioned may lieconveniently employed and, obviously.v other metals may prove satisfactory in practice. t

The coating may be employed in protection of ferrous metals during heat treatment at any temperature which is sufliciently high to result in oxidation of the protective metal.

It will be noted that while we have referred to, and prefer, application of the coating by electro-plating, such coating might, of course, be applied in other manners as, for example, by applying the metal in a molten state orby "dipping; in tin coating, the metal might be immersed in a solution containing tin and cream of tartar.

We claim:

1. The method of producing uncoated articles of heat-treated ferrous metal comprising coating the same prior to heat treatment with a metal 1 0 of the group tin, zinc and cadmium, subjecting the metal to a working step producing the coating to an extremely fine thickness and then heattreating the metal at a temperature and in an atmosphere converting the coating to an oxide lightly adherent to the ferrous metal.

2. The method of producing uncoated articles of heat-treated ferrous metal comprising coating the same prior to heat treatment with tin, subjecting the metal to a working step producing 4. The method oi producing uncoatedarticles of heat-treated ferrous metal comprising coating the same prior to heat treatment with cadmium, subjecting the metal to a working step producing the coating to an extremely nne thickness and then heat-treating the metal at a temperature and in an atmosphere converting the coating to an oxide lightly adherent to the ferrous metal.

ELLWOOD IVINS. HORACE 8. HRCHER. 

